Liquid scintillation counters measure charged particle-emitting radioactive isotopes and are used for environmental studies, nuclear chemistry, and life science. Alpha and beta emissions arising from the material under study interact with the scintillation cocktail to produce light. The prototypical liquid scintillation counter employs low-level photon-counting detectors to measure the arrival of the scintillation light produced as a result of the dissolved material under study interacting with the scintillation cocktail. For reliable operation the counting instrument must convey the scintillation light to the detectors efficiently and predictably. Current best practices employ the use of two or more detectors for coincidence processingmore » to discriminate true scintillation events from background events due to instrumental effects such as photomultiplier tube dark rates, tube flashing, or other light emission not generated in the scintillation cocktail vial. In low background liquid scintillation counters additional attention is paid to shielding the scintillation cocktail from naturally occurring radioactive material (NORM) present in the laboratory and within the instruments construction materials. Low background design is generally at odds with optimal light collection. This study presents the evolution of a light collection design for liquid scintillation counting in a low background shield. The basic approach to achieve both good light collection and a low background measurement is described. The baseline signals arising from the scintillation vial are modeled and methods to efficiently collect scintillation light are presented as part of the development of a customized low-background, high sensitivity liquid scintillation counting system.« less

A discussion of the limits imposed by thermodynamics on the collection of light from scintillation counters by photocathodes is given, and a method for concentrating the light energy to any degree is pointed out. The method employs a fluorescent material to slightly reduce the photon energy and thus to emit fluorescence. A light pipe-fluorescent converter-light pipe arrangement for increasing light intensity is discussed. (D.L.C.)

Several methods of collecting light on scintillation counters using WLS fibers and WLS bars were studied. Nearly 20 prototype counters with different designs and with sizes ranging from 14x11x1.3 cm{sup 3} to 105x60x1.3 cm{sup 3} have been tested using cosmic muons and radioactive source. The efficiency of light collection on number of photoelectrons, uniformity of response, and time resolution have been measured. Test results for two new designs of light collection from scintillator based on WLS fibers around perimeter of scintillator plate and WLS fibers placed in machined on scintillator plate deep grooves are presented. Two out of the studiedmore » designs have been chosen as the basic options for the Doe muon system upgrade: light collection using two WLS bars for the forward muon scintillation counters and light collection using WLS fibers in deep grooves on scintillator for central area muon counters.« less

The use of light guides to improve routine tritium counting efficiency was investigated. By optimizing the tritium spectrum with respect to the discriminators and using an effective light guide, a differential tritium counting efficiency of 44% can be obtained for routine use. Counting errors arising from varying sample volumes and condensation on the vial are eliminated by use of the light guide. (auth)